Phenylethylamine derivatives

ABSTRACT

Trifluoromethylthiophenylethylamine derivatives, made from the corresponding acid chlorides by successive reduction, condensation with nitroethane, reduction, and condensation with an amine, possess anorexigenic properties, unaccompanied by central stimulant activity or cardiovascular effects.

This application is a continuation-in-part of our copending application, Ser. No. 365,181 filed on May 30, 1973 and now U.S. Pat. No. 3,965,190, granted June 22, 1976.

The present invention provides the phenylethylamine derivatives of the formula: ##STR1## in which R₁ and R₂ are identical or different and represent hydrogen atoms or straight or branched alkyl radicals of 1 to 5 carbon atoms, or R₁ and R₂, together with the nitrogen atom, form a heterocyclic radical which may contain one or more other hetero-atoms, for example a piperidino, morpholino or thiomorpholino radical, and A represents sulphur or oxygen, and their acid addition salts with pharmaceutically acceptable organic and inorganic acids.

In view of the existence of an asymmetric carbon atom in the molecule of the compounds of formula (I), they exist in racemic and optically active forms, and it is to be understood that all such forms are within the scope of the invention.

Pharmacological investigation of the compounds of formula (I), as the hydrochlorides, has shown that they possess powerful anorexigenic properties. However, unlike the majority of amphetamine derivatives, they are devoid of (1) central stimulant activity, especially at the level of the cortex; and (2) cardiovascular effects such as tachycardia and increase in the arterial pressure. These properties make the compounds of formula (I) and their salts very valuable in therapy, especially for the treatment of various forms of obesity.

The invention thus includes within its scope pharmaceutical compositions comprising a compound of formula (I), as base or pharmaceutically acceptable salt thereof, and a compatible pharmaceutical carrier, especially one such as to provide a composition suitable for oral administration, e.g. as a pill, tablet, powder, syrup or elixir.

According to a feature of the invention, the compounds of formula (I) are prepared by condensing a 1-phenyl-2-propanone of the formula: ##STR2## in which A is as hereinbefore defined, with an amine of formula: ##STR3## in which R₁ and R₂ are as hereinbefore defined, and, if desired, converting a base obtained into an acid addition salt thereof.

This condensation is preferably carried out at elevated temperature in the presence of formic acid, using a large excess of the amine, preferably at 160° to 170° C. for 10 to 20 hours, preferably about 14 hours. The compound of formula (I) may be isolated either as a base or as a salt, preferably the hydrochloride.

The compounds of formula (II) are new. They are prepared by reducing a 1-phenyl-2-nitro-propene of the formula: ##STR4## in which A is oxygen or sulphur, for example with a mixture of iron and hydrochloric acid, in the presence of ferric chloride. This reduction is preferably carried out at 90° C., by heating for a few hours at this temperature. The 1-phenyl-2-nitro-1-propene may be isolated by steam distillation after the reaction mixture has been rendered alkaline.

The 1-phenyl-2-nitro-propenes of formula (IV) are also new. They are made by condensing a benzaldehyde of the formula: ##STR5## in which A is oxygen of sulphur, with nitro-ethane in the presence of a catalytic amount of an aliphatic amine, for example n-butylamine. This reaction may be carried out by heating the mixture at the reflux temperature of nitro-ethane and separating the water produced as it is formed.

The aldehydes of formula (V) are also new. They are made by reducing a benzoic acid chloride of the formula: ##STR6## in which A is oxygen or sulphur, with hydrogen in the presence of palladium, for example, in toluene, in the presence of a catalytic amount of 5% strength palladium on barium sulphate. The temperature of the reaction is the reflux temperature of the solvent employed, and its duration is from 10 to 15 hours, preferably about 12 hours. The aldehyde of formula (V) is isolated by combining it with sodium bisulphite, and then decomposing the compound obtained by heating in water in the presence of potassium carbonate and steam distillation of the aldehyde (V).

According to another feature of the invention, the compounds of formula (I) in which R₁ and R₂ represent simultaneously hydrogen atoms may also be prepared by transforming a 1-phenyl-2-propanone of formula (II) into its oxime and then reducing the oxime into the primary amine of formula (I).

The oximes are made by reacting the ketone II with a hydroxylamine salt, e.g. hydrochloride, in a polar solvent, for example an alcohol, in the presence of a light alkaline reagent such as an alkaline acetate. The reduction of the oximes may be carried out via chemical or catalytic route, preferably hydrogenizing with rising hydrogen in the presence of Raney alloy.

The amines of formula (I) may be resolved into their optical antipodes by any known means, for example by fractional crystallization of their salts with an optically active acid, preferably d-tartaric acid or d-dibenzoyltartaric acid.

The following examples illustrate the invention.

EXAMPLE 1 : 1-(3'-Trifluoromethylthio-phenyl)-2-ethylamino-propane. (a) 3-Trifluoromethylthio-benzaldehyde

A solution of 56.9 g (237 mmols) of 3-trifluoromethyl-thiobenzoic acid chloride in 285 ml of anhydrous toluene and 5.7g of 5 percent strength palladium on barium sulphate is introduced into a 1 liter three-necked flask equipped with a condenser, a mechanical stirrer and a gas bubbler tube. This mixture is heated, with stirring, for 12 hours at the reflux temperature, while a gentle stream of hydrogen is bubbled through it. The catalyst is filtered off and washed with diethyl ether. 125 ml of a solution of sodium bisulphite (d = 1.33) are added to the filtrate. This mixture is stirred vigorously for 24 hours and the bisulphite compound is filtered off, washed with diethyl ether and introduced into a three-necked flask. A solution of 80 g of potassium carbonate in 500 ml of water is added and the mixture is boiled, so as to steam distill the aldehyde as it is formed. The distillate is extracted twice in succession with diethyl ether. The combined ether phases are dried over sodium sulphate and filtered. The solvent is evaporated in vacuo on a water bath and the residue is rectified. 33.3g (67 % yield) of 3-trifluoromethylthio-benzaldehyde, as an oil, b.p. 108°-111° C./30-38 mm.Hg, are thus obtained.

    ______________________________________                                         Analysis C.sub.8 H.sub.5 F.sub.3 OS (M.W. = 206)                               Calculated % :   C 46.60   H 2.45                                              Found % :        46.54     2.41                                                                 46.35     2.46                                                ______________________________________                                    

(b) 1-(3'-Trifluoromethylthio-phenyl)-2-nitro-1-propane.

33.3 g (16 mmols) of 3-trifluoromethylthiobenzaldehyde, 43.3 ml of nitro-ethane and 2 ml of n-butylamine are introduced into a 250 ml flask equipped with a Dean and Stark trap surmounted by a condenser. The mixture is heated for 4 hours at the reflux temperature and then rectified. After the nitro-ethane has been removed, 26.8 g (64 % yield) of 1-(3'-trifluoromethylthio-phenyl)-2-nitro-1-propene, b.p. 130°-138° C./8-9 mm.Hg, are collected. This compound is dissolved in petroleum ether (b.p 35°-70° C) and the solution is chilled overnight. 1-(3'-Trifluoromethylthio-phenyl)-2-nitro-1-propene is finally obtained as a crystalline solid, m.p. 48° C.

    ______________________________________                                         Analysis C.sub.10 H.sub.8 F.sub.3 NO.sub.2 S (M.W. = 263)                      Calculated % :   C 45.63   H 3.06                                              Found % :        45.55     3.13                                                                 45.50     2.85                                                ______________________________________                                    

(c) 1-(3'-Trifluoromethylthio-phenyl)-2-propanone

13.2 g (50 mmols) of 1-(3'-trifluoromethylthio-phenyl)-2-nitro-propene, 19.6 g (0.35g atom) of iron powder and 0.25 g of ferric chloride are introduced into a 250 ml three-necked flask equipped with a mechanical stirrer, a condenser and a dropping funnel and this mixture is heated on an oil bath at 80°-90° C. 13.5 ml of concentrated hydrochloric acid are added dropwise, via the dropping funnel, with stirring, over the course of 7 hours, while the temperature is kept at 90° C. The reaction mixture is allowed to cool and rendered alkaline with sodium hydroxide solution. The ketone is then steam distilled. The distillate is extracted twice in succession with 100 ml. of diethyl ether each time. The two ether extracts are combined, dried over sodium sulphate and filtered. The solvent is evaporated from the filtrate in vacuo on a water bath, and the residue is rectified. 7.1g (60.5 % yield) of 1-(3'-trifluoromethylthio-phenyl)-2-propanone are thus obtained as a colourless oil, b.p. 138°-146° C/25-30 mm.Hg, n_(D) ²³° = 1.489.

    ______________________________________                                         Analysis C.sub.10 H.sub.9 F.sub.3 OS (M.W. = 234)                              Calculated %     C 51.28   H 3.88                                              Found %          50.99     3.90                                                                 51.29     3.66                                                ______________________________________                                    

(d) 1-(3'-Trifluoromethylthio-phenyl)-2-ethylamino-propane

1.85 g (40 mmols) of formic acid are introduced into a 50 ml two necked flask equipped with an air condenser and a dropping funnel. The flask is cooled on an ice bath and 2 ml of ethylamine are added dropwise. The reaction mixture is allowed to return to ambient temperature and 2.85 g (10 mmols) of 1-(3'-trifluoromethylthio-phenyl)-2-propanone are added. The contents of the flask are heated for 14 hours at 160°-170° C, 2 ml of concentrated hydrochloric acid and 2 ml of water are added, and the mixture is heated for 3 hours at the reflux temperature. A further 2 ml of concentrated hydrochloric acid are added and the mixture is heated again at the reflux temperature for 2 hours. The mixture is allowed to cool, water is added and the product is extracted once with 50 ml of diethyl ether. The aqueous layer is rendered alkaline with sodium hydroxide solution and extracted three times in succession with 50 ml of diethyl ether each time. The combined ether extracts are washed several times with water, dried over sodium sulphate, and filtered. The ether is evaporated from the filtrate in vacuo on a water bath. The 1.4 g of oily residue are dissolved in anhydrous diethyl ether and a solution of hydrogen chloride in diethyl ether is added until precipitation has ended.

1-(3'-Trifluoromethylthio-phenyl)-2-ethylaminopropane hydrochloride, recrystallized from ethyl acetate, is obtained as a white crystalline compound which is soluble in water, m.p. 130° C. Yield : 30 percent.

    ______________________________________                                         Analysis C.sub.12 H17ClF.sub.3 NS (M.W. = 299.8)                               Calculated % :                                                                            C 48.07  H 5.71   N 4.67 Cl 11.83                                   Found % :  48.19    5.67     4.66   11.97                                                 48.15    5.62     --     11.87.                                     ______________________________________                                    

EXAMPLE 2 : 1-(3'-Trifluoromethoxy-phenyl)-2-ethylaminopropane and its hydrochloride (a) 3-Trifluoromethoxy-benzaldehyde

103 g (0.544 mol) of stannous chloride and 400 ml of diethyl ether are introduced into a 1 liter three-necked flask equipped with a condenser, a mechanical stirrer and a gas bubbler tube. This mixture is cooled and saturated with hydrogen chloride gas until the stannous chloride is completely dissolved. A solution of 72.7 g (0.388 mol) of 3-trifluoromethoxy-benzonitrile in 75 ml of anhydrous diethyl ether is added dropwise but fastly via the dropping funnel, while the mixture is cooled with ice-water. The mixture is allowed overnight, then the aldehyde is steam distilled. The distillate is extracted several times with diethyl ether and the extracts are combined. 250 ml of a solution of sodium bisulphite (d= 1.32-1.33) are added to the extracts and allowed overnight. The bisulfite compound is filtered off, washed with a small quantity of ice-water and then with diethyl ether. The compound is introduced into a 1 liter flask which contains solution of 60 g of potassium carbonate in 250 ml of water. The mixture is heated at 100° C so as to decompose the bisulfite compound and to steam distill the aldehyde as it is formed. The distillate is extracted several times with diethyl ether. The combined ether phases are dried over sodium sulphate and filtered and the solvent is evaporated. 32g (44 % yield) of 3-trifluoromethoxy-benzaldehyde are obtained as a colourless oil.

(b) 1-(3'-Trifluoromethoxy-phenyl)-2-nitro-1-propene

32 g (0.17 mol) of 3-trifluoromethoxy-benzaldehyde, 32 ml of nitro-ethane and 2 ml of n-butylamine are introduced into a 100 ml flask surmounted by a condenser. The mixture is heated for 20 hours at the reflux temperature and then rectified. 29 g (70 % yield) of 1-(3'-trifluoromethoxy-phenyl)-2-nitro-1-propene are collected as a yellow oil b.p. 90°-110° C./2mm Hg.

(c) 1-(3'-Trifluoromethoxy-phenyl)-2-propanone.

29 g (117 mmols) of 1-(3'-trifluoromethoxyphenyl)-2-nitro-propene, 46g (0.82 g atom) of iron powder, 0.6 g of ferric chloride and 120 ml of water are introduced into a 500 ml three-necked flask equipped with a mechanical stirrer, a condenser and a dropping funnel, and this mixture is heated at 80° C. 29 ml of concentrated hydrochloric acid are added dropwise, via the dropping funnel, with stirring, over the course of 5 hours, while the temperature is kept at 80° C. The reaction mixture is allowed to cool overnight. The ketone is then steam distilled. The distillate is extracted twice in succession with 100 ml of diethyl ether each time. The two ether extracts are combined, dried over sodium sulphate and filtered. The solvent is evaporated from the filtrate in vacuo on a water bath, and the residue is rectified. 14, 15 g (55 % yield) of 1-(3'-trifluoromethoxy-phenyl)-2-propanone are thus obtained as a liquid, b.p. 112° -118° C/18 mm.Hg, n_(D) ²¹°5 = 1.448.

(d) 1-(3'-Trifluoromethoxy-phenyl)-2 ethylamino-propane and its hydrochloride.

13 ml (0.2 mol) of ethylamine are introduced into a 250 ml two-necked flask equipped with an air condenser and a dropping funnel and cooled on an alcohol-carbon dioxide ice bath. 9.65 ml (0.25 mol) of formic acid are added dropwise. The reaction mixture is allowed to return to ambient temperature and 14.15g (65 mmols) of 1-(3'-trifluoromethoxy-phenyl)-2-propanone are added. The contents of the flask are heated for 20 hours at 150° C. After cooling 20 ml of concentrated hydrochloric acid and 20 ml of water are added, and the mixture is heated for 5 hours at the reflux temperature. A large amount of water is added and the product is extracted with 100 ml of diethyl ether. The aqueous layer is rendered alkaline with sodium hydroxide solution and extracted three times in succession with 100 ml of diethyl ether each time. The combined ether extracts are washed several times with water, dried over sodium sulphate, and filterd. The ether is evaporated from the filtrate in vacuo on a water bath.

The residue is rectified.8,7 g (70 % yield) of 1-(3'-trifluoromethoxy-phenyl)-2-ethylamino-propane are thus obtained as a liquid, b.p. 108°-110°/16 mm Hg.

Analysis C₁₂ H₁₆ F₃ NO (M.W. = 247.27): Calculated %: C, 58.31; H, 6.56; N, 5.66. Found %: C, 58.58; H, 6.67; N, 5.59.

To prepare the hydrochloride, the above base is dissolved in anhydrous diethyl ether and a solution of hydrogen chloride in diethyl ether is added until precipitation has ended, so as to obtain 1-(3'-trifluoromethoxy-phenyl)-2-ethylamino-propane hydrochloride, m.p. 132° C.

Analysis C₁₂ H₁₇ ClF₃ NO (M.W. = 283.8): Calculated % : C,5.80; H, 6.04; Cl,12.49. Found % : C,5.83; H,5.77; Cl,12.52.

EXAMPLE 3 : 1-(3'-Trifluoromethylthio-phenyl)-2-amino-propane and its hydrochloride

(a) Method I

3.5 g (0.2 mol) of liquid ammoniac are introduced into 250 ml two-necked flask equipped with an air condenser and a dropping funnel and cooled on an alcohol-carbon dioxide ice bath. 9.7 ml of formic acid are added dropwise via the dropping funnel. The reaction mixture is allowed to return to ambient temperature and 15.1 g (65 mmols) of 1-(3'-trifluoromethylthio-phenyl)-2-propanone are added. The contents of the flask are heated for 23 hours at 155°-160° C. After cooling 30 ml of concentrated hydrochloric acid are added, and the mixture is heated for 7 hours at the reflux temperature. A large amount of water is added and the product is extracted with 100 ml of diethyl ether. The aqueous layer is rendered alkaline with sodium hydroxide solution and extracted three times in succession with 100 ml of diethyl ether each time. The combined ether extracts are washed several times with water, dried over sodium sulphate, and filtered. The ether is evaporated from the filtrate in vacuo on a water bath. 8 g (52 % yield) of 1-(3'-trifluoromethylthio-phenyl)-2-amino-propane are thus obtained as a slightly yellow oil.

Analysis C₁₀ H₁₂ F₃ NS (M.W. = 235.27): Calculated % C,51.05; H,5.14; F,24.23; N,5.95; S,13.63. Found % C,51.12; H,5.03; F,24.75; N,6.04; S,13.29.

The above base is dissolved in anhydrous diethyl ether and a solution of hydrogen chloride in diethyl ether is added until precipitation has ended so as to obtain 1-(3'-trifluoromethylthio-phenyl)-2-amino-propane hydrochloride.

Analysis C₁₀ H₁₃ Cl F₃ NH (M.W. = 271.73): Calculated % C,44.20; H, 4.82; Cl,13.05; F,20.98; N,5.18; S,11.80. Found % C,44.17; H,4.90; Cl,12.92; F,21.30; N,5.00; S,12.02.

(b) Method II

(i) oxime of the 1-(3'-trifluoromethylthiophenyl)-propanone.

17.8g (0.076 mol) of 1-(3'-trifluoromethylthiophenyl)-propanone, 17.8 g (0.256 mol) of hydroxylamine hydrochloride and 17.8 g (0.13 mol) of sodium acetate in absolute ethanol are introduced into a 500 ml flask equipped with an air condenser. The solution is heated at the reflux temperature for 5 hours, the alcohol is evaporated on a steam-bath under vacuum, the residue is triturated in water and extracted several times with diethyl ether. The ether extracts are washed with water, dried over sodium sulphate, filtrated and the solvent is evaporated from the filtrate. The residue is recrystallised from hexane.

9.3 g (yield 49 %) of the oxime are obtained m.p. 84° C.

(ii) 1-(3'-trifluoromethylthio-phenyl)-2-amino-propane hydrochloride.

9.3 g (0.037 mol) of the oxime of the 1-(3'-trifluoromethylthio-phenyl)-propanone, 200 ml of absolute ethanol and 200 ml of sodium hydroxide 1N are introduced in a 1l flask cooled with an ice water bath.

While stirring the solution, 20 g of Raney alloy are introduced, within 7 hours, by small amounts. The mixture is stirred 2 hours after the addition, the nickel is filtrated, washed with ethanol; the solvent is evaporated from the filtrate on a steam-bath under vacuum. The residue is extracted several times with diethyl ether, the ethereal extracts are collected, extracted three times successively with diluted hydrochloric acid. The hydrochloric extracts are alkalinized by sodium hydroxide and extracted again two times successively with diethyl ether. These two last ethereal extracts are collected, washed with water, dried over sodium sulphate, filtrated and the solvent is evaporated under vacuum on a steam-bath.

4.9 g of 1-(3'-trifluoromethylthio-phenyl)-2-amino-propane, in the form of a colourless oil which is solubilized in anhydrous diethyl ether, are obtained.

A current of gaseous hydrochloric acid is driven through the solution.

The hydrochloride obtained is crystallized by dissolution in benzene and slow addition of diethyl ether.

4.7 g (yield 47 %) of the hydrochloride of the 1-(3'-trifluoromethylthio-phenyl)-2-amino-propane are obtained. Soluble in water. m.p. 130°-140° C.

Analysis C₁₀ H₁₃ ClF₃ NS (271.73): Calculated % C,44.20; H, 4.82; Cl,13.05. Found % C,44.52; H,5.03; Cl,13.04.

EXAMPLE 4 : 1-(3'-Trifluoromethylthio-phenyl)-2-n-propylamino-propane and its hydrochloride.

9.25 g (0.2 mol) of formic acid are introduced into a 250 ml two-necked flask equipped with an air condenser and a dropping funnel. The flask is cooled on an ice bath at 0° C and 11.8g (0.2 mol) of n-propyl-amine are added dropwise within 30 minutes. The reaction mixture is allowed to return to ambient temperature and 14.25 g (0.06 mol) of 1-(3'-trifluoromethylthio-phenyl)-2-propanone are added. The contents of the flask are heated for 14 hours at 160° C (internal temperature), 10 ml of concentrated hydrochloric acid and 10 ml of water are added, and the mixture is heated for 3 hours at the reflux temperature. A further 10 ml of concentrated hydrochloric acid are added and the mixture is heated again at the reflux temperature for 2 hours. The mixture is allowed to cool, 250 ml of water and 250 ml of diethyl ether are added. The precipitate is strained, suspended again in water; sodium hydroxide is added to the suspension, the separated oil is extracted with diethyl ether, the ether solution is washed with water and dried; the solvent is evaporated and the residue is rectified.

5.6 g (yield 33 %) of 1-(3'-trifluoromethylthiophenyl)-2-n-propylamino-propane are obtained as a colourless liquid.

b.p. 88°-90°/0.5 mm Hg. n_(D) ²³ = 1.478.

The hydrochloride is prepared in anhydrous diethyl ether and recrystallised from ethyl acetate. m.p. 152° C.

Analysis C₁₃ H₁₉ ClF₃ NS (M.W. = 313.8): Calculated % C,49.77; H,6.10; N,4.66. Found % C,49.69; H,6.55; N,4.47.

EXAMPLE 5 : 1-(3'-Trifluoromethylthio-phenyl)-2-isopropylamino-propane and its hydrochloride.

9.25 g (0.2 mol) of formic acid are introduced into a 250 ml two necked flask equipped with an air condenser and a dropping funnel. The flask is cooled on an ice bath at 0° C and 11.8g (0.2 mol) of isopropylamine are added dropwise within 30 minutes. The reaction mixture is allowed to return to ambient temperature and 14.25 g (0.06 mol) of 1-(3'-trifluoromethylthio-phenyl)-2-propanone are added. The contents of the flask are heated for 20 hours at 165° C (internal temperature). 10 ml of concentrated hydrochloric acid and 10 ml of water are added and the mixture is heated for 3 hours at the reflux temperature. A further 10 ml of concentrated hydrochloric acid are added and the mixture is heated again at the reflux temperature for 4 hours. The mixture is allowed to cool, the separated oil is extracted with water, the solution is neutralized with sodium bicarbonate, extracted with diethyl ether and the ether solution is dried over sodium sulphate and filtered.

A stream of hydrochloric acid is driven through the solution until precipitation has ended. The separated hydrochloride is strained and recrystallised from ethyl acetate.

2g (yield 20 %) of the hydrochloride of the 1-(3'-trifluoromethylthio-phenyl)-2-isopropylamino-propane are obtained. m.p. 126° C.

Analysis C₁₃ H₁₉ ClF₃ NS (313.81): Calculated % : C,49.77; H,6.10; N,4.46. Found % : C,49.78; H,6.22; N,4.43.

EXAMPLE 6 : 1-(3'-Trifluoromethylthio-phenyl)-2-n-amyl-amino-propane and its hydrochloride.

9.25 g (0.2 mol) of formic acid are introduced into a 250 ml two-necked flask equipped with an air condenser and a dropping funnel. The flask is cooled on an ice bath at 0° C and 17.4 g (0.2 mol) of n-amyl-amine are added dropwise within 30 minutes. The reaction mixture is allowed to return to ambient temperature and 14.25 g (0.06 mol) of 1-(3'-trifluoromethylthio-phenyl)-2-propanone are added. The contents of the flask are heated for 10 hours at 160° C. 10 ml of concentrated hydrochloric acid and 10 ml of water are added and the mixture is heated for 3 hours at the reflux temperature. A further 10 ml of concentrated hydrochloric acid are added and the mixture is heated again at the reflux temperature for 2 hours. The hot contents of the flask are poured into 250 ml of water, allowed to cool. The precipitate is strained, the soft crystals are splitted in 250 ml of diethyl ether, strained again and washed again with diethyl ether. The crystals are recrystallised from 250 ml of ethyl acetate.

9.7 g (yield 46.5%) of the hydrochloride of 1(3'-trifluoromethylthio-phenyl)-2-n-amyl-amino-propane are obtained. m.p. 161° C.

Analysis C₁₅ H₂₃ F₃ ClNS (341.87): Calculated % C, 52.70; H, 6.78; Cl, 10.38; N, 4.10. Found % C, 52.72; H, 6.80; Cl, 10.38; N, 4.09.

EXAMPLE 7 : 1-(3'-Trifluoromethylthio-phenyl)-2-isobutylamino-propane

9.25 g (0.2 mol) of formic acid are introduced into a 250 ml two necked flask equipped with an air condenser and a dropping funnel. The flask is cooled on an ice bath at 0° C and 14.6 g (0.2 mol) of isobutylamine are added dropwise, with stirring. The reaction mixture is allowed to return to ambient temperature and 14.25 g (0.06 mol) of 1-(3'-trifluoromethylthio-phenyl)-2-propanone are added. The contents of the flask are heated for 14 hours at 160°-165° C. 10 ml of concentrated hydrochloric acid and 10 ml of water are added and the mixture is heated for 3 hours at the reflux temperature. A further 10 ml of concentrated hydrochloric acid are added and the mixture is heated again at the reflux temperature for 2 hours. The mixture is allowed to cool, the organic phase is poured off, triturated in diethyl ether, the separated crystals are strained and washed with diethyl ether and recrystallised from ethyl acetate.

4 g (yield : 22 %) of the hydrochloride of the 1-(3'-trifluoromethylthio-phenyl)-2-isobutylamino-propane are obtained. m.p. 139°-140° C.

Analysis C₁₄ H₂₁ ClF₃ NS (327.8): Calculated % C, 51.32; H, 6.46; N, 4.27; Cl, 10.82. Found % C, 51.22; H, 6.34; N, 4.08; Cl 11.12.

EXAMPLE 8 : 1-(3'-Trifluoromethylthio-phenyl)-2-methylamino-propane and its hydrochloride.

A mixture of 11.8 g. (0.2 mol) of N-methyl-formamide and 2.5 g of formic acid is introduced into a 250 ml two-necked flask equipped with an air condenser and a dropping funnel. The mixture is heated to 165° C. 46.8 g (0.2 mol) of 1-(3'-trifluoromethylthio-phenyl)-propanone are added dropwise with stirring.

The contents of the flask are heated for 20 hours at 165° C, the excess of N-methyl-formamide and formic acid is evaporated. 50 ml of hydrochloric acid (50 %) are added to the residue and the mixture is heated for 8 hours at the reflux temperature.

The mixture is allowed to cool, 100 ml of water are added, the mixture is washed with 50 ml of benzene, filtrated on vegetal black. The filtrate is alkalinized with ammonia, extracted five times successively with 50 ml of diethyl ether. The extracts are washed with water and dried. The solvents are evaporated and hydrochloric ether is added to the oily residue. The separated hydrochloride is strained and recrystallized from a mixture (1/4) of ethyl acetate and diisopropyl ether.

5.5 g (yield : 31.2 %) of the hydrochloride of the 1-(3'-trifluoromethylthio-phenyl)-2-methylamino-propane in the form of micro-crystals are obtained. m.p. 92° C.

Analysis C₁₁ H₁₅ ClF₃ NS (285.5): Calculated % C, 46.30; H, 5.31; N, 4.90; Cl, 12.40. Found % C, 46.29; H, 5.23; N. 5.27; Cl 12.75.

Pharmacological investigation of the compounds has shown that they are very valuable in therapy.

In view of the lightening of the report, the investigated compounds are referred as follows:

A : compound of example 1 (hydrochloride)

B : compound of example 2 (hydrochloride)

C : compound of example 3 (hydrochloride)

D : compound of example 4 (hydrochloride)

E : compound of example 5 (hydrochloride)

F : compound of example 6 (hydrochloride)

The indexes r, d and l following these letters mean that the compounds are respectively in racemic, dextrarotatory or levorotatory form.

The investigation has shown that all of them but the two levorotatory isomers A₁ and B₁ possess powerful anorexigenic properties.

These properties have been displayed by measuring in strict standard conditions the food quantities absorbed by rats which were previously accustomed to receive their food every day within a 6 hours period. The experiments have been carried out by administering each compound in several doses and determining graphically the 50 % active dose DA 50 (doses able to reduce the consumption of food of 50 %). The compounds of this invention are compared to fenfluramine (in racemic form).

The following DA 50 were found:

    ______________________________________                                         compund          DA 50 (mg/kg)                                                 ______________________________________                                         Fenfluramine     10                                                            A.sub.r          4.5                                                           A.sub.d          2.5                                                           A.sub.1          >10                                                           B.sub.r          9                                                             B.sub.d          4.5                                                           B.sub.1          >10                                                           C.sub.r          5                                                             D.sub.r          2.5                                                           E.sub.r          2.5                                                           F.sub.r          3.5                                                           ______________________________________                                    

The anorexigenic activity of the dextrorotatory and certain racemic compounds is very high, up to four times that of fenfluramine. The other racemic compounds are also more active than fenfluramine and the results show that in fact their activity is due to the dextrorotatory isomer for the levo compounds are much less active.

The acute toxicity of the compounds is moderate and equal or slightly inferior to that of fenfluramine (even in the case of the most active compound) and is the same for the dextro or the levorotatory isomer.

As a result of these considerations, the compounds of the invention in racemic or dextrarotatory form possess a much better therapeutic index (up to four times) than fenfluramine.

These compounds are remarkable for the lack of the most characteristic secondary effects of amphetamine derivatives: on the one hand, they are devoid of central stimulent activity, which is shown by actimetry and group toxicity experiments; on the other hand, they are distinctive from any amphetamine derivative, including fenfluramine, by the lack of general hypertensive activity and especially by the lack of effects in the pulmonary arterial pressure.

    ______________________________________                                         anesthetized                                                                              increase in the arterial pressure                                   dog        carotid       pulmonary                                             ______________________________________                                         Fenfluramine                                                                              significant from                                                                             significant from                                                 0,5 mg/kg     1 mg/kg                                               A.sub.r    none up to    none up to 5 mg/kg                                               5 mg/kg                                                             A.sub.d    none or non   none or non signifi-                                             significant up                                                                               cant up to 2 mg/kg                                               to 2 mg/kg                                                          ______________________________________                                    

The compounds of this invention are thus remarkable both for their anorexigenic activity --which is higher than that of fenfluramine-- and for they are devoid of secondary effects. These properties make the compounds of formula (I) and their salts very valuable in therapy, especially for the treatment of various forms of obesity.

They may be administered via any usual route, but preferably oral route, in combination with excipients suitable for their administration. These pharmaceutical compositions can also contain other medicinal substances with which the compounds (I) are pharmaceutically and therapeutically compatible.

For oral use, the solid or liquid pharmaceutical forms appropriate for this type of administration are employed, but is to say tablets, dragees, gelatine-coated pills and the like, and the daily dose can vary between 10 to 50 mg. 

What we claim is:
 1. A phenylethylamine of the formula: ##STR7## wherein R₁ and R₂ are independently hydrogen or straight or branched-chain alkyl of 1 to 5 carbon atoms, in the racemic or optically active forms and the acid addition salts thereof.
 2. 1-(3'-Trifluoromethylthiophenyl)-2-ethylamino-propane in racemic or optically active forms, and its pharmaceutically acceptable acid addition salts.
 3. 1-(3'-Trifluoromethylthiophenyl)-2-amino-propane in racemic or optically active forms and its acid addition salts.
 4. 1-(3'-Trifluoromethylthiophenyl)-2-n-propylamino-propane in racemic or optically active forms, and its pharmaceutically acceptable acid addition salts.
 5. 1-(3'-Trifluoromethylthiophenyl)-2-isopropylamino-propane in racemic or optically active forms, and its pharmaceutically acceptable acid addition salts.
 6. 1-(3'-Trifluoromethylthiophenyl)-2-n-amylamino-propane in racemic or optically active forms, and its pharmaceutically acceptable acid addition salts.
 7. 1-(3'-Trifluoromethylthiophenyl)-2-isobutylamino-propane in racemic or optically active forms, and its pharmaceutically acceptable acid addition salts.
 8. 1-(3'-Trifluoromethylthiophenyl)-2-methylamino-propane in racemic or optically active forms, and its pharmaceutically acceptable acid addition salts. 